The invention relates to anti-friction mountings for rotating shafts and more particularly to a mounting for carrying the axial and radial load of a compressor of the helical screw type. In a compressor of this type having a driven male rotor intermeshing with a female rotor the compression of the fluid between the rotors results in a high load in an axial direction. Thus in compressors of this type a thrust bearing has been used on each rotor shaft to maintain the rotors at a fixed noncontacting position between the end covers and to absorb the axial load. See for example, the patent to Lysholm U.S. Pat. No. 2,243,874.
A problem associated with the use of an axial thrust bearing independent of the radial load bearing, in the prior art, has been the absorption of some of the radial load by the thrust bearing. This subjects it to a type of load for which it is not designed and can lead to a malfunction or shortened life.
Furthermore, in a helical compressor of the type under consideration the clearance between the end faces of the rotors and the discharge end of the housing is critical as a determinate of the performance of the compressor.
Various kinds of bearing mountings for both radial and axial loads have been used heretofore in which an attempt has been made to compensate for the differences in the loadings.
Breckheimer U.S. Pat. No. 4,119,392 discloses a screw compressor with a short axially shiftable rotor carried by a roller bearing and an axially displaceable bearing which is directly engaged by a piston, the operation of which controls the position of the rotor.
The patent to Langner, U.S. Pat. No. 3,738,719, discloses a preloaded bearing in which a spring produces a preload value against the outer races of a coaxial bearing.
Hanson, U.S. Pat. No. 1,399,959 employs a compressible material instead of a spring with adjustment for preloading.
The German patent, No. 2,807,411 of 1978, discloses a bearing providing for preloading and rotor expansion.
Witte, U.S. Pat. No. 1,161,570 discloses a bearing mounting for use in line shaft hangers of different types.
Roggenburk, U.S. Pat. No. 2,762,340, employs a two-row ball set at each end for providing both radial and axial centering, in which each carries a portion of both loads.
Stoica, U.S. Pat. No. 3,429,228, employs a single-row ball bearing at each end to take the radial and thrust load, claiming thereby elimination of thrust bearings.
Schibbye, U.S. Pat. No. 3,467,300, discloses a helical screw type compressor with male and female rotors and which employs the thrust of the low pressure helical screws to counterbalance the thrust of the high pressure helical screws of a two stage compressor, and thus eliminate any heavy thrust load. Centering is obtained by thrust collars.
Ware, U.S. Pat. No. 3,528,757, employs an adjustable thrust collar to center the rotor.
Snider, U.S. Pat. No. 3,719,440, employs a Belleville type spring to provide preloading of two single-row radial bearings which handle both radial and thrust loads.
Hansson, U.S. Pat. No. 3,804,562, has a single-row radial bearing at one end of a shaft which is adjustable for centering of the rotor. At the opposite end of the shaft is another single-row ball bearing with the inner race positioned by a Belleville type spring, thus causing a preloaded thrust centering of the rotor, with both bearings carrying equal axial and thrust loading.
Beavers, U.S. Pat. No. 4,033,647, discloses thrust bearings which carry the vertical shaft loading. The bottom bearing carries a predetermined load and when the load is exceeded the top bearing carries the excess. Radial loading is insignificant and is carried by sleeves.
Lohneis, U.S. Pat. No. 3,454,313, discloses force preloading of a radial load carrying bearing and tapered thrust rings to compensate for shaft temperature changes and other axial loading. The single-row bearings must carry the axial load up to the limits of expansion of the thrust rings.